The present invention relates to cementing operations and, more particularly, to lightweight settable compositions comprising water, cement kiln dust (“CKD”), and microspheres, and associated methods of use.
Settable compositions may be used in a variety of above ground (e.g., in the construction industry) and subterranean applications. As used herein, the term “settable composition” refers to any composition that over time will set to form a hardened mass. One example of a settable composition comprises hydraulic cement and water. Subterranean applications that may involve settable compositions include, but are not limited to, primary and remedial cementing. For example, settable compositions may be used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a settable composition may be pumped into an annular space between the subterranean formation and the pipe string disposed therein. The settable composition sets in the annular space, thereby forming an annular sheath of hardened cement (e.g., a cement sheath) that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Settable compositions also are used in remedial cementing operations such as plugging highly permeable zones or fractures in well bores, plugging cracks and holes in pipe strings, and the like.
In some instances, settable compositions utilized in subterranean operations may be lightweight, for example, to prevent excessive hydrostatic pressure from being exerted on subterranean formations penetrated by the well bore, whereby the formations may be unintentionally fractured or the hole may collapse. One type of lightweight settable composition is a foamed cement composition, e.g., a cement composition that comprises a surfactant and a gas. Additionally, lightweight additives (e.g., microspheres) also may be added to settable compositions to reduce the density thereof.
During the manufacture of cement, a waste material commonly referred to as “CKD” is generated. “CKD,” as that term is used herein, refers to a partially calcined kiln feed which is typically removed from the gas stream and collected in a dust collector during the manufacture of cement. Usually, large quantities of CKD are collected in the production of cement that are commonly disposed of as waste. Disposal of the waste CKD can add undesirable costs to the manufacture of the cement, as well as the environmental concerns associated with its disposal. The chemical analysis of CKD from various cement manufactures varies depending on a number of factors, including the particular kiln feed, the efficiencies of the cement production operation, and the associated dust collection systems. CKD generally may comprise a variety of oxides, such as SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O, and K2O.